As user's demand for digital broadcasting services providing high quality audio and video services increases, currently Digital Audio Broadcasting (DAB) programs are being broadcast or trial broadcast in many countries and regions including Europe and the United States of America, etc. Also, in Korea, terrestrial and satellite Digital Multimedia Broadcasting (DMB) services are provided.
FIG. 1 is a diagram to explain the concept of a conventional satellite broadcasting system.
Referring to FIG. 1, a satellite broadcasting system includes a broadcasting station 100, a satellite base station 110, a satellite 120, a satellite control station 130, a broadcasting receive terminal 140, and a gap filler 150.
The satellite base station 110 receives broadcast data from each broadcasting station 100 and transmits it to the satellite 120 through a Ku band (12.5-18 Ghz) uplink transmission line. The broadcasting station 100 transmitting the broadcast data to the satellite 120 through one or more satellite base station 110 may be plural.
Then the satellite 120 amplifies the Ku band broadcast signal received from the satellite base station 110, and converts it into an S band broadcast signal. The converted S band broadcast signal is sent out toward a service coverage together with the Ku band broadcast signal.
The satellite control station 130 monitors and controls operating state of the satellite 120.
The broadcasting receive terminal 140 located within a satellite broadcasting service coverage receives a broadcast signal from the satellite 120 to reproduce a broadcasting program. However, in an area with signal attenuation caused by shadowing or blocking by buildings, shields or masks, etc., the gap filler 150 relays and transmits a broadcast signal. That is, the gap filler 150 receives and converts a Ku band Time Division Multiplexing (TDM) signal from the satellite 120 into an S band Code Division Multiplexing (CDM) signal, and sends out them. The broadcasting receive terminal 140 located within a satellite broadcasting service coverage demodulates a higher power signal among the S band CDM signal from the satellite 120 and the S band CDM signal received via the gap filler 150, and reproduces it. The broadcasting receive terminal 140 may be a portable terminal (e.g., a mobile communication terminal, Personal Data Assistance (PDA), automobile-based terminal, etc.).
FIG. 2 is a diagram to explain the general frame structure of a base band transmission signal of a gap filler.
Referring to FIG. 2, a frame structure consists of 12.75 ms basic frames. 6 basic frames constitute 1 super frame of 76.5 ms. Each broadcasting channel is embedded on the QPSK signal composed of 816 bytes (6528 bits), which consists of 408 bytes for I (In-Phase) channel and 408 bytes for Q (Quadrature-phase) channel. A pilot channel allocated with Walsh Code 0 is used for frame synchronization and control data transmission, and Pilot Symbol (PS) and control data (Di) are formed in 25□ units, respectively. A single pilot channel frame is configured with 102 blocks of 32 bits (i.e. 125□, 2048 chips). That is, one pilot channel frame is composed of 51 pilot symbols and 51 control data (Di, i=1,2, . . . , 51) in total. The first control data D1 in the pilot channel is a unique word for frame synchronization. Pilot symbol is sent out in sequence of “1111111 11111111 11111111 11111111” and unique word D1 is sent out in sequence of “1101010 10110101 01011001 10001010”. PS and D1 are pilot data the broadcasting receive terminal 140 recognizes.
FIG. 3 is a block diagram to explain the configuration of a conventional transmission system for satellite broadcasting.
Referring to FIG. 3, a satellite broadcasting transmission system comprises Reed-Solomon (RS) encoders (210a, . . . , 210n, and 210m), byte interleavers (220a, . . . , 220n, and 220m), convolution encoders (230a, . . . , 230n, and 230m), bit interleavers (240a, . . . , and 240n), and a CDM modulator (250).
For independent broadcasting by broadcasting stations 100 and/or contents, the satellite broadcasting transmission system can transmit broadcast data up to 63 channels by using orthogonal spreading codes which are different from each other, and transmits received sync data and control data through pilot channels. Error correction coding system utilizes RS-Convolution concatenated codes, while error spread method utilizes byte/bit interleaving. Channel-encoded signals are subjected to a modulation operation in the CDM modulator 250. For modulation, the broadcasting channel adopts a QPSK system with a roll-off factor 0.22, and the pilot channel adopts a BPSK system.
FIG. 4 is a block diagram to explain the configuration of a conventional receiving system for satellite broadcasting.
Referring to FIG. 4, a satellite broadcasting receiving system comprises tuners (310a and 310b), a CDM Demodulator (320), a Bit Deinterleaver (330), Viterbi Decoders (340a and 340b), Byte Deinterleavers (350a and 350b), RS Decoders (360a and 360b), a multiplexer MUX (370), and so on. While FIG. 4 illustrated a system with a plurality of tuners 310a and 310b, if a portable terminal is concerned, antenna diversity may not be implemented after giving consideration to its size and portability.
The CDM Demodulator 320 includes rake fingers that synthesize a signal by Maximal Ratio Combining (MRC) etc., according to power (or intensity) and delay of the signal, and despreads it by a Walsh code of a desired broadcasting channel.
Output signals of the CDM Demodulator 320 are divided into broadcast channel signals and pilot channel signals. The broadcast channel signals go through a channel decoding process and restored to audio data and video signals. The pilot channel signals go through a pilot channel decoding process and used as control data of the broadcasting receive terminal 140.
In general, satellite DMB using the satellite broadcasting transmission/receiving systems discussed earlier can cover broader areas than the terrestrial DMB. Also, the gap filler 150 may be used additionally in an urban area (especially downtown) where signal receive environment is relatively poor. Depending on a shadow area using the gap filler 150, however, a signal being received in a multipath channel environment is sometimes delayed and its frequency is spread. Consequently, a spread code of the received signal may not be orthogonal any more and Multi User Interface (MUI) may occur. In such case, desired broadcast information is not restored accurately.
Therefore, a chip equalization apparatus has been used in replace of the CDM Demodulator 320, and a chip equalizer in the apparatus is designed to be able to compensate a distorted channel by performing the channel compensation on complex weights of taps of the chip equalizer. In code division multiple access (CDMA) wireless system, the signal receive configuration requires as many chip equalizers as time delay in the multi-path channel so as to compensate channel distortion that is caused by multi-path channel. Although a long chip equalizer may be needed in the multi-path channel, it may cause other problems, e.g., the receiver becomes bulky and power consumption increases considerably, or the convergence speed of tap coefficients can be lowered.